The following are mentioned as belonging to the prior art:
U.S. Pat. No. 4,516,977 to Herbert (D1), PA1 EP-A-0 136 848 to Baxter Travenol Laboratories, Inc.(D2) and PA1 WO-A-82/04016 also to Baxter Travenol Laboratories, Inc.(D3).
Connecting arrangements or connecting techniques with which the present invention is concerned are disclosed, inter alia, in D1. The object of D1 is a medical bag for storing blood or infusion solutions, in which a connecting piece made of a dimensionally stable plastic material is inserted into the body of the bag made of a different plastic material, wherein, to produce a firm and fluid-tight connection between bag and connecting piece, a bonding layer made of a non-crosslinked copolymer made from an olefin and vinyl acetate or polyurethane is arranged between the connecting piece and the sections of the body of the bag found to be in contact with it.
For the medical bag in accordance with D1, plastic materials based on polyolefins are suggested, inter alia those based on polyethylene, polypropylene and polybutylene. In addition to these homopolymers, plastic materials are also mentioned in D1 that are substituted olefins containing, for example, methyl, ethyl, vinyl or halogen substituents. Copolymers or blends of corresponding materials are also suggested.
Polyethylenes with average to high densities, high molecular weights and narrow molecular weight distributions are particularly preferred for the bag. Furthermore, according to D1, care should be taken to ensure, in this case, that the polyolefins have a melting point below the sterilization temperature of 110 to 120.degree. C.
Suitable plastics for use for connecting pieces or inserts (in accordance with D1), are relatively rigid and transparent plastic materials and are deformed only at a pressure of at least 2 bar, for example rigid PVC, polypropylene, polyamide, polycarbonate, polyester, polyacrylates and similar materials and/or copolymers based on the previously mentioned compounds and styrene-containing copolymers, but in particular polycarbonates.
Materials for the bonding layer include, according to D1, copolymers of an olefin with vinyl acetate or a polyurethane. The bonding layer is between 0.1 and 7 mm thick and, to produce a connection between the connecting fittings piece or insert and bag, is arranged so that a length of tubing of the bonding layer material is drawn over or brushed onto the exterior of the insert or connecting tube, then the insert is pushed into the opening provided for it in the bag and finally the whole unit is welded together.
It is also possible to weld the bonding layer to the connecting piece first, for fixing purposes, and then to introduce this into the prepared connector opening in the bag and seal this unit. In this case, after the welding procedure, the bonded system is autoclaved at approximately 120.degree. C. and 2 bar. During the heat-sealing process itself (welding), the bag is bonded to the ethylene/vinyl acetate copolymer in the intermediate layer, the bag also preferably being made of polycarbonate, like the connecting piece.
The connecting technique in accordance to D1 is disadvantageous for a number of reasons. On the one hand the interpositioning of a connecting layer between the separate parts of the system to be connected is a relatively complicated procedure. On the other hand, the bag is not suitable for recycling due to the use of different materials (the bonding layer is not made of a polyolefin material).
The object of D2 is another connecting technique. This discloses a flexible bag made of ethylene/vinyl acetate copolymers (EVA), in which a multi-layered connection tube made of a plastic material is arranged so that it is in fluid connection with the interior of the bag, wherein the tube has an outer layer which contains an ethylene/vinyl acetate copolymer which can be connected to the internal surface of the bag. In this case the seal is preferably achieved by means of a high frequency energy sealing process. Apart from the fact that the multi-layered tubes, connecting pipes or fittings have PVC-containing layers, wherein PVC is not a material which gives no concern during waste disposal procedures, and furthermore which almost always contains plasticizer which can diffuse out of the material into the solution being stored, a mixture of PVC and vinyl acetate is very difficult to separate during recycling procedures.
D3 also discloses a connector designed specifically for connecting two different plastic materials as an intermediate layer which is particularly suitable for connecting medical containers such as, for instance, blood bags to flexible tubes, when the parts to be connected consist of materials which are incompatible with each other so that direct welding of the separate parts to each other is not possible.
The intermediate item in accordance with D3 is a coextruded or injection moulded multi-layered connector with layers made of different plastic materials, wherein one of the layers "melts" at a lower temperature than the others.
D3 mentions polyvinylchloride as the material in the inner connector layer, whereas the outer layer consists of a lower melting polymer, for example polyethylenevinylacetate (EVA). In this embodiment, the connector in accordance with D3 is suitable, for instance, for connecting a PVC tube to a polyethylene container whose connecting piece consists of a material containing propylene units and polyethylenevinylacetate units as the first and second components.
To form the connection, the PVC tube is now placed in contact with the inner layer of the connector, for example using a solvent such as cyclohexanone. The outer layer of the connector is then introduced into the connection section of the bag under sliding contact, after firmly fixing the inner tube/connector link. The entire tube/connector/connecting piece/bag arrangement is then taken up to a temperature which is sufficient to melt the EVA in the external layer of the connector and to bond with the connecting piece. This thermal treatment can be performed, inter alia, in an autoclave.
To bond separate parts made of similar materials and to lower the temperature required to heat-bond them, D3 suggests the use of two connectors, the first with a low-melting plastic material outer layer (EVA) and a higher melting plastic material inner layer (PVC) and a second with the reverse sequence of layers. The two connectors with different diameters are then pushed together so that the PVC layers are in contact with each other. The two PVC layers are then solvent-sealed (cyclohexanone) together. The resulting "double connector" then has two low-melting plastic material outer layers which can be used in a known manner for connecting EVA bags and tubes.
In several ways, the disclosure published in D3 is also associated with disadvantages for the person skilled in the art.
On the one hand, at least one additional connector part is required each time to connect a medical system (bag+tube). On the other hand, in the end at least two steps are always required to produce the connection. Thus solvent-welding of the PVC layers in the connector and the tube or even of two connectors regularly precedes heat-treatment, which is really quite a complicated procedure. Finally, D3 is directed exclusively towards classical PVC and EVA materials which, from a current point of view, appear rather dubious, especially against the background of the plasticizer problems associated with PVC.